Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
DOI: https://doi.org/10.29363/nanoge.nipho.2019.023
Publication date: 21st November 2018
The outstanding efficiencies of organic-inorganic perovskite thin film based solar cells led to interest in increasing the range of perovskite materials. One such family of materials is the all inorganic CsPbX3 colloidal nanocrystals (NCs). Despite the recent surge of synthetic protocols producing different shapes and crystal structures, there are still significant gaps in the understanding of their formation mechanism. Here we try to address the growth mechanism and reveal the importance of the ligand shell on determining the size, habit and phase.
We have identified that the formation of CsPbX3 NCs follows through two separate stages. First, seed mediated nucleation through the formation of metal Pb NCs. Second, further growth is attained through oriented attachment. We show the impact of delicate changes in the ligand environment on the stoichiometry and crystal structure of cesium lead halide perovskites NCs. We show that small changes in the oleate:ammonium ratio generated by the addition of a Lewis base determines the size, shape and crystallographic structure of CsPbX3 NCs. Using this understanding we could synthesize materials such as CsPbBr3 nanowires, CsPbCl3 bulk-like crystals and CsPbI3 orthorhombic nanowires of length ranging from 200 nm to several microns. Moreover, we show how a robust reversible transformation that involves also a stoichiometric change, from cubic CsPbX3 to rhombohedral Cs4PbX6 which can be achieved via control of the OA to OLAm Brønsted acid−base type equilibrium. We present surface analysis revealing the differences in the ligand shell of cubic CsPbBr3 versus Cs4PbBr6. In addition, we show evidence that the transition mechanism involves an exfoliation and recrystallization processes. This mechanism is supported by crystallographic data showing a Cs4PbBr6, 0D layered rhombohedral phase. The formation of a layered Cs4PbBr6 habit indicates a direct path for transformation that is controlled by thermodynamic surface stabilization provided by the ligand shell.
Finally, we discuss the use of these materials in hybrid semiconductor systems.
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